Today's internal combustion engines include tank venting systems, in which fuel evaporated in the tank is stored in an active carbon filter, which is connected to the induction pipe of the internal combustion engine via a tank venting valve capable of being closed off. In response to opening the tank venting valve, air is drawn in via a connection of the active carbon filter to the environment, the air entraining the temporarily stored fuel and supplying it for combustion. Using the tank venting valve, the amount of gas drawn in is controlled in such a manner, that on one hand, the active carbon filter is sufficiently flushed with air, and on the other hand, no intolerably large disturbances to the fuel-air ratio of the mixture supplied to the internal combustion engine occur.
To comply with legal regulations, a defective tank venting valve installed in a tank venting system must be recognized as defective, using suitable diagnoses. It is known that correct opening of the tank venting valve may be checked by activating the tank venting valve so as to open, without the overall system taking this opening activation into consideration. Thus, in the control unit of the internal combustion engine of the tank venting valve, no consideration is given to the proportion of air and fuel that is supplied to the engine, via the tank venting valve, when it is activated so as to open. It may be inferred that a tank venting valve is intact or defective, using the reaction of the induction pipe pressure to this occurring disturbance variable, which causes a change in pressure.
A defect is present, when the difference between the induction pipe pressure after the opening activation of the tank venting valve and prior to the opening activation of the tank venting valve is below a particular threshold value. In the case of a tank venting valve that is jammed shut, then, for example, activating the tank venting valve so as to open does not open the valve, which means that no change in pressure occurs in the induction pipe. The ascertained pressure difference is zero, and a defect of the tank venting valve is detected.